A team of Japanese scientists managed to bring one of the long-term humanity dreams into life: battery that charges itself by using sunlight.

Amazing, isn’t it?

Now the only thing that you need is the Sun and…that’s all.

Instead of plugging into a separate solar panel, the translucent battery functions both as a rechargeable battery and as a photovoltaic cell.

Let’s talk more about this masterpiece.

Translucent lithium-ion battery from Japanese masterminds

A group of Japanese researchers led by Mitsunobu Sato, president of Kogakuin University and professor at the Department of Applied Physics, School of Advanced Engineering of the university, has developed a translucent Li-ion battery and announced it in a thesis in 2013.

Then,2 years after that, there were made some changes to the materials of the translucent Li-ion battery ,so that electrons excited by light coming to the negative electrode can be used to charge the battery.

And ,at the trade show, the group showed the results of an experiment in which optical charge and discharge are repeated five times by applying near-ultraviolet light with an output of 10mW/cm2, which is about 1/10 that of sunlight.

The battery was exhibited at Innovation Japan 2015, a trade show that took place from Aug 27 and 28, 2015, in Tokyo.

A few words about physics of the battery

The main component of the electrolyte used for the positive electrode of the battery is Li3Fe2 (PO4)3 (LFP). And those of the electrolyte used for the negative electrode are Li4Ti5O12 (LTO) and LiPF6 (lithium hexafluorophosphate). Those materials are commonly used for Li-ion rechargeable batteries.

Nonetheless, oxides are basically transparent, and the thicknesses of the positive and negative electrodes are only 80nm and 90nm, respectively, realizing a high light transmittance.

The light transmittance for green light (wavelength: about 550nm) is about 60% after discharging.

It lowers to about 30% after charging because the density of lithium changes at the electrodes and the electronic state (valence) of the material changes.

The output voltage of the battery is about 3.6V and the battery itself has 20 charge-discharge cycles.

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Plans for the future

With the battery, the group aims to realize a "smart window," which is an almost transparent window that functions both as a large-area rechargeable battery and as a photovoltaic cell (when the window receives sunlight, it is pigmented, lowering light transmittance).

Well, let’s hope it will be this way.

At least, the battery definitely has the potential to turn existing automative market upside down and change our world for better.